The present invention relates to wafers used for the selective connecting and disconnecting of plastic tubes such as would be used in total containment welding devices which have been described in various patents. The wafer is used in such systems as the component for heating the plastic tubes either as part of a process which disconnects a single tube and forms two tube sections for later welding of at least one of the tube sections to a tube section of a different tube. When used for the connect process the wafer applies heat to separate tube ends causing the tube ends to melt so that the melted ends could be pressed together and form a unitary tube.
Frequently the selective connecting and disconnecting of plastic tubes is performed in connection with medical techniques. Under certain circumstances it is necessary that the wafer be a single use wafer. The United States Food and Drug Administration, for example, has requirements prohibiting multiple use of devices such as wafers under certain conditions.
U.S. Pat. No. 5,525,186 discloses a particularly advantageous manner of assuring that a wafer can be used only once. As described in that patent the wafer is provided with an aperture into which a sensing material is located. During the connect/disconnect operation the wafer moves past a sensor. When the sensor detects the presence of the material in the aperture the process continues. If, however, no material is in the aperture, the absence of the material is sensed and the process is halted by deactivating the device. The particular sensing material disclosed in the '186 patent is a material which melts upon being heated. Thus, when a wafer is being used for the first time the sensing material is initially in the aperture and detected by the sensor. Subsequently, when the wafer is heated the sensing material melts and there is no longer any material in the aperture. If an attempt is made to reuse the same wafer the sensor would detect the absence of the material or the open hole or aperture.
U.S. Pat. No. 5,871,612 discloses the provision of a sensing or fuse material in the aperture wherein the sensing material has one set of light transmission characteristics prior to heating and different light transmission characteristics after the wafer is heated. Thus, a sensor would sense the proper light transmission characteristics for a wafer which has not yet been heated and would also sense the different light transmission characteristics which result after the wafer has been heated. This differs from the '186 patent in that with the Pat. '186 patent after the wafer is heated the material melts and the aperture becomes completely open. With the Pat. '612 patent, however, after the wafer is heated material still remains in the aperture but has different light transmission characteristics than it had before heating. The sensing material of the '612 patent is a two layer laminate which includes a clear base material, such as mylar, having a coating of a material having limited light transmission characteristics, such as aluminum. The material is placed in the hole or aperture of the copper wafer. When the wafer is heated the material melts thereby allowing light to pass through the fuse hole. While the fuse material of the '612 patent represents a distinct advancement in the art, there are some disadvantages which could affect its efficiency. For example, if the aluminum layer becomes too greatly scratched such as from coating wind up, slitting or punch press tooling, the scratching will cause wide variations in the optical density. Additionally, because of the two layer nature of the laminate care must be taken to properly orient the layers with respect to the sensors.